Convert
このページを編集する際は，編集に関する方針に従ってください． 概要 *gcc-4.1.0/gcc/c-convert.cにて定義 * C 言語レベルの型変換．ちなみに c-convert.c には，この関数しかない． 1 /* Language-level data type conversion for GNU C. 41 /* Change of width--truncation and extension of integers or reals-- 42 is represented with NOP_EXPR. Proper functioning of many things 43 assumes that no other conversions can be NOP_EXPRs. 44 45 Conversion between integer and pointer is represented with CONVERT_EXPR. 46 Converting integer to real uses FLOAT_EXPR 47 and real to integer uses FIX_TRUNC_EXPR. 48 49 Here is a list of all the functions that assume that widening and 50 narrowing is always done with a NOP_EXPR: 51 In convert.c, convert_to_integer. 52 In c-typeck.c, build_binary_op (boolean ops), and 53 c_common_truthvalue_conversion. 54 In expr.c: expand_expr, for operands of a MULT_EXPR. 55 In fold-const.c: fold. 56 In tree.c: get_narrower and get_unwidened. */ 57 58 /* Subroutines of `convert'. */ 59 60 61 62 /* Create an expression whose value is that of EXPR, 63 converted to type TYPE. The TREE_TYPE of the value 64 is always TYPE. This function implements all reasonable 65 conversions; callers should filter out those that are 66 not permitted by the language being compiled. */ 引数 * tree type ** 型を表すノード (式の型を，この型に変換する) * tree expr ** 式を表す木構造 実装 68 tree 69 convert (tree type, tree expr) 70 { 71 tree e = expr; 72 enum tree_code code = TREE_CODE (type); 73 const char *invalid_conv_diag; 74 75 if (type error_mark_node 76 || expr error_mark_node 77 || TREE_TYPE (expr) error_mark_node) 78 return error_mark_node; 79 80 if ((invalid_conv_diag 81 = targetm.invalid_conversion (TREE_TYPE (expr), type))) 82 { 83 error (invalid_conv_diag); 84 return error_mark_node; 85 } 86 87 if (type TREE_TYPE (expr)) 88 return expr; 89 90 if (TYPE_MAIN_VARIANT (type) TYPE_MAIN_VARIANT (TREE_TYPE (expr))) 91 return fold_build1 (NOP_EXPR, type, expr); 92 if (TREE_CODE (TREE_TYPE (expr)) ERROR_MARK) 93 return error_mark_node; 94 if (TREE_CODE (TREE_TYPE (expr)) VOID_TYPE) 95 { 96 error ("void value not ignored as it ought to be"); 97 return error_mark_node; 98 } 99 if (code VOID_TYPE) 100 return build1 (CONVERT_EXPR, type, e); 101 #if 0 102 /* This is incorrect. A truncation can't be stripped this way. 103 Extensions will be stripped by the use of get_unwidened. */ 104 if (TREE_CODE (expr) NOP_EXPR) 105 return convert (type, TREE_OPERAND (expr, 0)); 106 #endif 107 if (code INTEGER_TYPE || code ENUMERAL_TYPE) 108 return fold (convert_to_integer (type, e)); 109 if (code BOOLEAN_TYPE) 110 { 111 tree t = c_objc_common_truthvalue_conversion (expr); 112 if (TREE_CODE (t) ERROR_MARK) 113 return t; 114 115 /* If it returns a NOP_EXPR, we must fold it here to avoid 116 infinite recursion between fold () and convert (). */ 117 if (TREE_CODE (t) NOP_EXPR) 118 return fold_build1 (NOP_EXPR, type, TREE_OPERAND (t, 0)); 119 else 120 return fold_build1 (NOP_EXPR, type, t); 121 } 122 if (code POINTER_TYPE || code REFERENCE_TYPE) 123 return fold (convert_to_pointer (type, e)); 124 if (code REAL_TYPE) 125 return fold (convert_to_real (type, e)); 126 if (code COMPLEX_TYPE) 127 return fold (convert_to_complex (type, e)); 128 if (code VECTOR_TYPE) 129 return fold (convert_to_vector (type, e)); 130 if ((code RECORD_TYPE || code UNION_TYPE) 131 && lang_hooks.types_compatible_p (type, TREE_TYPE (expr))) 132 return e; 133 134 error ("conversion to non-scalar type requested"); 135 return error_mark_node; 136 }